1. Field of the Invention
The present invention relates to longwall mining in general.
More particularly, the invention relates to walking mine supports, and specifically to devices of this type which support the transitional area between road (gallery) and face.
2. The Prior Art
Longwall mining is well known. A review of the techniques employed and the equipment used may be found in U.S. Bureau of Mines Information Circular 8740, to which reference may be had for background information.
Basically, coal-mining equipment in longwall mining moves in a roadway (gallery) along a mine face from which coal is removed and transported away along the roadway. The roadway is supported by longitudinally spaced stationary supports each having uprights at opposite sides of the roadway and a lintel-type roof shield. The coal at the face is often so located that it must be removed by undercutting the face, i.e. by removing coal along the lower part of the face which leaves an overhang. This overhang, including the part of the face which merges with the roof of the adjacent roadway, must be supported against collapse. Also, since during passage of the coal-mining equipment the uprights of the stationary supports must be temporarily removed at the mine-face side of the roadway, the transitional area between roadway and face must similarily be supported by auxiliary supporting equipment.
For purposes of such support it is known to provide auxiliary supporting equipment which, heretofore, was a type that could be clamped, bolted or otherwise connected to the roadway supports. This equipment includes e.g. supporting shields and other elements which are braced from below by pit props. As coal removal progresses along the mine face, this equipment must frequently be disassembled, moved along the mine face to new locations and be reassembled. Given the relative frequency of such moves and the relatively large member of components involved in assembly and disassembly, it is clear that such operation are time-consuming and highly labor-intensive. Moreover, the frequent moves tend to change the equilibrium of the overburden so that disassembly and reassembly of the equipment usually requires the ability to make on-the-spot improvisation to accommodate for unexpected or changing conditions. This, in turn, means that the operations must be carried out by skilled miners, rather than by auxiliary personnel, and makes the whole procedure even more costly. In addition, damage to the various components, as well as to the coal-mining and coal-conveying equipment and to the roadway supporting equipment, is almost unavoidable. This is costly and, in the case of damage to the roadway supports, makes it even more difficult to carry out the assembly and disassembly operations.
The seam area of the face adjacent the roadway (i.e. the aforementioned transitional area) is also the area in which the drive equipment for the coal-mining and coal-conveying machines is located. This is the reason for the need to remove the stationary uprights while this equipment passes through. Because of this it has heretofore been customary to temporarily support this transitional area by means of individual hydraulic pit props which, in effect, define a kind of travelling buffer zone between the face and the roadway supports. The term "travelling" here denotes the fact that after the mining equipment has passed a given location, the pit props are moved along with it and in the vacated location the stationary uprights are reinstalled. Again, the release and resetting of these pit-props is carried out manually. Aside from the cost and the loss of time involved, the setting of these props (and the effectiveness of support offered by them) is directly dependent on the skill and care of the miners who are entrusted with this job. Any human error thus necessarily increases the danger of cave-ins. Also, the frequent removal of the props tends to cause loosening of the rock strata of the overburden in the transitional area between face and roadway.
A proposal has been made to provide a supporting arrangement for this transitional area which was to be coupled to and move with a face support and a walking roadway support. However, this could not be employed in practice because severe damage was constantly being sustained and also because it was incapable of accommodating itself to the constantly changing conditions of the surrounding strata.